1. Field of the Invention
The present invention relates to a test socket that is used in testing a semiconductor integrated circuit (hereinafter abbreviated as IC when appropriate). In particular, the invention relates to a structure of contact pins, and a manufacturing method thereof, that are incorporated in a socket and brought into contact with the respective leads of an IC.
2. Background Art
FIGS. 5-8 show a contact pin of a conventional test socket that is used in testing a semiconductor integrated circuit or the like. FIG. 5 is a perspective view showing the structure of a tip portion of a conventional contact pin. FIGS. 6 and 7 are sectional views showing contact states of an IC lead and the contact pin of FIG. 5. FIG. 8 is a sectional view of a tip portion of the contact pin of FIG. 5 and shows its materials and structure.
As shown in FIG. 5, the conventional contact pin 30 is configured in such a manner that a contact portion 32 having a flat contact surface 33 is provided at the tip of a base portion 31 that exhibits spring action as a whole.
As shown in FIG. 6, an IC 15 is tested by bringing the contact surfaces 33 of the contact pins 30 into contact (electrical contact) with leads 16 of the IC 15.
In performing a test, particularly a final test, on an IC, in many cases, the leads of the IC have been plated with solder for subsequent mounting on a printed circuit board. An IC good/defective judgment is made by performing an electrical characteristic test in a state that electrical connections are established by bringing the contact pins of a socket into contact with the leads of the IC in such a state.
As the above IC test is repeated, as shown in FIG. 7, solder fragments 17 of the IC leads 16 are accumulated on the surfaces of the contact pins 30 and the leads 16 come into contact with the solder fragments 17. This causes a problem that the dispersion and the magnitude of the contact resistance increase.
FIG. 8 is a sectional view showing the materials and the structure of the contact portion 32 of the conventional contact pin 30. In FIG. 8, reference numeral 21 denotes a pin spring base member made of beryllium copper or the like, numeral 22 denotes a nickel plating undercoat (nickel thin film) of several micrometers in thickness, and numeral 23 denotes a gold plating layer (gold thin film) of 0.2-0.3 xcexcm in thickness.
That is, to have a small electrical resistance value and not to be oxidized under a low-temperature or high-temperature environment so as to exhibit insulation resistance, in most cases, socket contact pins are manufactured by plating the beryllium copper contact base member 21 having resilience first with nickel and then with gold.
While the gold plating layer 23 has advantages that, for example, it has a small electrical resistance value in various environments and is not oxidized in a low-temperature or high-temperature environment so as to exhibit insulation resistance, it has disadvantages that it is prone to form oxides with tin and lead that are components of plated solder of IC leads (i.e., it is prone to cause what is called a xe2x80x9csolder transitionxe2x80x9d phenomenon) and, in particular, lead oxide increases the electrical contact resistance and cause a contact failure (connection failure) as deterioration with age.
Although plating layers other than the gold plating layer, such as a nickel plating layer, a tin plating layer, a silver plating layer, and a rhodium plating layer, are used for special purposes, they have the common problems as stated below.
As described above, in general, conventional contact pins have level contact surfaces that are to be brought into contact with IC leads or the like, and are used in such a state. Therefore, solder fragments of IC leads tend to deposit on the contact surfaces of contact pins.
Further, since the surfaces of conventional contact pins are plated with gold, a phenomenon tends to occur that solder plating layers of IC leads cause xe2x80x9csolder transitionxe2x80x9d on the surfaces of the contact pins. This phenomenon increases the contact resistance value and may cause a connection failure, to prevent an electrical characteristic test from being performed correctly. As a result, the production yield is lowered or it becomes necessary to perform operations of xe2x80x9ccleaningxe2x80x9d and xe2x80x9cpolishingxe2x80x9d to remove oxides of tin and lead, which lowers the productivity and requires extra costs.
The present invention has been made to solve the above problems in the conventional art, and an object of the invention is therefore to provide contact pins, as well as a test socket having such contact pins, that are free of a problem that solder plating layers of ICs cause the xe2x80x9csolder transitionxe2x80x9d on the surfaces of the contact pins to cause a contact failure or the like.
Another object of the invention is to provide a manufacturing method of the above test socket.
According to one aspect of the present invention, a test socket for an electronic circuit device has a contact pin that is to be brought into electrical contact with a lead of the electronic circuit device, and a contact surface of the contact pin to contact the lead assumes a curved surface.
In another aspect of the present invention, the contact pin is preferably formed by coating a surface of a contact pin base member with a gold thin film, then with a nickel or titanium thin film, and then with a tungsten, chromium, or titanium thin film.
In another aspect of the present invention, the contact pin is preferably formed by coating a surface of a contact pin base member made of beryllium copper, phosphor bronze, or spring steel with a nickel or titanium thin film, and then with a tungsten, chromium, or titanium thin film.
Other and further objects, features and advantages of the invention will appear more fully from the following description.